The burgeoning field of wireless multimedia devices and the appetite for high-bandwidth multimedia content have led to a challenging home networking environment. In a marked move away from analog TV and DVDs, multimedia is increasingly being consumed through the network portal, and produced or hosted inside the home, bringing higher loads of performance-sensitive traffic to the home network. Further, by design and use, home media servers, set-top boxes and personal devices such as phones and tablets send and receive traffic mostly on wireless links. Amplifying the scarcity of capacity on the wireless medium, there is increased volume and diversity of traffic (multimedia, data, home monitoring and automation traffic, etc.) transmitted via the access point (AP). Thus, the AP, being the relay for all wireless traffic, must assume the role of ensuring throughput assurances for traffic identified as being important. Moreover, home networks are often unmanaged and host a variety of different devices from different vendors. Therefore, a viable solution must be automated, widely compatible and have a simple end-user interface.
There has been an effort by the IEEE 802.11 standards and the Wi-Fi Alliance to address the issue of multimedia traffic in Wi-Fi networks. The prioritized-QoS defined by IEEE 802.11e HCF-EDCA does not provide throughput guarantees, but only provides classes of traffic differentiation, where traffic of higher priority have a statistical advantage in the competition for medium access. With this approach, based on random access, each station decides which traffic to prioritize and thus the number of transmitters competing in the same traffic class is neither predictable nor controllable. The IEEE 802.11e standard has also defined a centralized approach, HCF-HCCA, to provide parameterized-QoS, which has never been adopted by Wi-Fi card vendors. Two main areas of work related to SHAPE have been studied: the medium access mechanisms of Wi-Fi networks and centralized traffic management.
In medium access the IEEE 802.11 standard defines a distributed random medium access mechanism (DCF), a polling-based medium access mechanism (PCF) and a hybrid solution (HCF) including a prioritized distributed random medium access (HCF-EDCA) and a polling-based medium access mechanism (HCF-HCCA). DCF, implemented in every Wi-Fi-certified device, aims for per-transmitter fairness and does not provide any traffic differentiation or prioritization. As the Wi-Fi Alliance does not provide a certification process for PCF and HCF-HCCA, these are rarely implemented in off-the-shelf products. HCF-EDCA, part of the IEEE 802.11e standard, is fairly widely accepted and aims at providing prioritized QoS. Some flavors of HCF-EDCA are certified by Wi-Fi Alliance as Wi-Fi Multimedia (WMM) capabilities, or Wireless Media Extension (WME) and devices with such implementations are generally referred to as QoS-enabled. The scheduled medium access (HCF-HCCA) defined by IEEE TGe was never certified and it is not commonly available. Other extensions such as direct link setup (DLS) have not been certified either.
In a non-QoS WLAN, IEEE 802.11 DCF provides statistically equal transmission opportunities to each transmitter. This per-transmitter fairness is known to produce unexpected results in the presence of heterogeneous stations such as transmitters using different raw bit rates. This is known in the art as the rate anomaly problem.
The prioritized-QoS defined by HCF-EDCA does not provide throughput guarantees, but only differentiates classes of traffic, where traffic of higher priority has a statistical advantage in the competition for medium access. Moreover, the effectiveness of the prioritization provided by HCF-EDCA depends on the medium access parameters (primarily the AIFS) adopted by each station for each class of traffic. In particular, it has been experimentally shown that in the case where a single station receives traffic tagged as background, while several stations transmit and receive traffic tagged as voice, the quality of the VoIP calls is acceptable only when the prioritized traffic accesses the medium with an AIFS parameter at least 6 slots shorter than that of the single background traffic flow. However, FIG. 1 shows, the default AIFS values used by non-QoS IEEE 802.11 devices is a SIFS plus 2 slots and that of best effort QoS traffic is a SIFS plus 3, and thus, higher priority traffic cannot use an AIFS that is 6 slots shorter. As a consequence, high priority traffic will only be able to obtain some share of the bandwidth available in the WLAN, and this will be further shared among all the high priority transmitters. Therefore, despite the statistical advantage, WMM WLANs cannot provide throughput guarantees to multimedia flows.
IEEE HCF-HCCA provides parameterized-QoS by having stations perform scheduled medium access with access control. Although some research has been devoted to solve the related scheduling problem, it is believed that this technology has never been deployed in off-the-shelf devices for the wireless home network. Further, the lack of a certification process suggests that a deployment of such technology is not imminent. TDMA medium access mechanisms are also able to enforce a centrally determined schedule. One prior art scheme designed a TDMA MAC for wireless mesh networks, using IEEE 802.11 hardware. All of these QoS enabling solutions assume station compliance. In contrast, SHAPE provides per-link bandwidth reservation, requiring no modification, nor compliance, of unaware legacy stations.
The recently standardized IEEE 802.11n has also attempted to address the issue of allocation of resources (transmission opportunities). For instance, the reverse direction grant (RDG) allows the AP, at the end of its transmission, to hand over transmission time to a station. This is, however, best-suited to bi-directional traffic and further requires the station to be compliant with the newer versions of the standard. It is, thus, not suitable for unidirectional multimedia traffic and for legacy devices.
The use of CTS frames as a silencing technique, outside the legacy RTS-CTS exchange, has recently gained increasing interest. Another prior art scheme proposed a micro-probing technique, where several APs in an enterprise WLAN synchronously transmit CTS-to-self frames to silence all the stations in a wide area and then perform quick link probing experiments in order to speed up the computation of interference graphs, while avoiding network downtimes. Yet another prior art scheme proposes Virtual PCF, in which unsolicited CTS are transmitted from an AP to a VoIP station, in order to silence the other stations and reduce the jitter experienced by VoIP packets.
Centralized traffic management in wireless enterprise networks is an active research area. Initially work focused on simplifying management and avoiding configuration errors. Lately, the interest has shifted towards solving performance problems particular to wireless networks, such as scheduling of conflicting links. Little attention has been paid to small unmanaged home networks, which today host a number of bandwidth-demanding devices. One prior art scheme studied the problem of traffic management in home networks, from an end-host perspective and not limited to the wireless network.